There is already a lot of information available online about using Cole Parmer peristaltic pumps to feed a calcium reactor. However, when I decided that a peristaltic pump was best way to consistently feed my Geo 612 calcium reactor, I ran into difficulties finding a Cole Palmer pump that was a good value. So, in the end, I decided to buy a Watson Marlow pump. Since I bought a relatively new model, I didn't end up saving versus the Cole Parmer solutions out there but I am happy with the purchase. Watson Marlow pumps are well-known for their reliability. In fact, they were specifically mentioned 15 years ago as a reliable feed pump: http://www.reefkeeping.com/issues/2002-05/sh/feature/ After some research, I narrowed down my search to the 500 series of pumps. I eventually settled on a Watson Marlow 520 pump, which is adjustable between 0 and 220 rpm. It can be adjusted by 0.1 rpm increments, which is a tremendous benefit for fine tuning reactor flow. I believe that all the Watson Marlow pumps are brushless, which is a concern on many of the Cole Parmer pumps. I ran into a bit of difficulty researching the differences between the various 520 pumps. Eventually, I came across this info: 520S has manual only control. It can be calibrated to display flowrate in ml/min 520U has manual, remote auto, and analogue control. It can be calibrated to display flowrate in ml/min 520Du has manual, remote auto, and RS232 control. It cannot be calibrated to display flowrate in ml/min After a bit of research, I bought a very clean Watson Marlow 520S pump with a 520R head off Ebay. While it was advertised for almost $1300, I managed to get one discounted for about 1/2 of the requested price. The pump is in near perfect shape and it’s built like a tank. Unlike some peristaltic pumps that can only use specific sizes of tubing, compatible tubing for these pumps is determined by the tubing wall thickness. My pump head accepts 1.6mm, which equates to 1/16" wall thickness. In the guide, it states the flow rates associated with various bores (inside diameter) of the tubing. So, I decided to forgo the expensive Watson Marlow tubing and went with the tubing recommended on a Reef Central thread for the Cole Parmer pumps since it is also 1/16" wall thickness. In the end, it worked perfectly but only time will tell regarding longevity. Here the links to the tubing and the parts I used to attach the pump the calcium reactor (these are the specific parts recommended by tkeracer619 on RC: Tygon PharMed Tubing http://www.usplastic.com/catalog/item.aspx?itemid=25534 1/8"FNPT x 1/4"Hose ID Polypropylene Female Adapter http://www.usplastic.com/catalog/item.aspx?itemid=36204 1/4" Tube OD x 1/8" MNPTF Connector http://www.usplastic.com/catalog/item.aspx?itemid=42009 Snap Grip Clamp http://www.usplastic.com/catalog/item.aspx?itemid=34082 I ordered the tubing and connectors from US Plastics and everything went together easily. I couldn't believe how quiet the pump is at lower rpms. I can’t even hear the pump unless I take off the front pump head guard. After installing the tubing and connectors, I calibrated the pump to show an accurate flow. Calibration was quite easy since all you need to do is run the pump into a graduated cylinder or measuring cup and input the amount that was dispensed. Here is how the pieces fit together: Using the 1/4“ ID tubing, the pump flow is approximately 7.4 ml per revolution. Given that the manual states that the flow should be approximately 7 ml/min per rpm, this about what I expected. As I’ve been tweaking my calcium reactor to dial-in the ideal alkalinity, I’ve had to change the flow rate a couple of times, which only takes seconds each time. Lately I’ve been running the pump at 3.0 rpm, which is 22.1 ml/min. The pump has been running flawlessly for the past two weeks. My only complaint so far is that the pump is quite large and takes a lot of space in my cabinet. If I had a heated garage, I would locate the pump and the calcium reactor out in the garage but right now that isn’t an option. Let me know if you have any questions. Since these pumps are so reliable and bullet-proof, I hope that this is last feed pump I’ll ever need to buy.